This invention relates to a fuel tank system for a direct ethanol injection octane boosted gasoline engine.
As described in U.S. patent application Ser. No. 10/991,774 filed on Nov. 18, 2004 and application Ser. No. 11/100,026 filed Apr. 6, 2005, on-demand octane boost using direct ethanol injection can be used to enable high fuel economy in two types of vehicle operation. The contents of these applications are incorporated herein by reference. In the first, the vehicle is essentially powered by gasoline (with a minimal amount of ethanol used for on-demand octane boost). In another mode of operation when the cost and availability of ethanol make its use attractive, the vehicle is powered by a flexible fuel mix of E85 and gasoline. In this case, the E85 can constitute up to 100% of the fuel. In contrast to the use of ethanol as a fuel that is blended with gasoline, the driver has the freedom to determine when and how much ethanol to use. As will be described below, the amount of ethanol or E85 required to be stored in a separate tank for on-demand octane boost is on the order of only 4 to 20 gallons per year when a vehicle is essentially powered by gasoline. The requirement is less when the vehicle is powered by a flexible fuel mixture of ethanol or E85 and gasoline. The ethanol can be added using either 1.0 to 2.5 gallon containers or by the use of a pump at the growing number of E85 fueling stations in the United States. This small amount of ethanol could be provided for 50 million vehicles using less than 1 billion gallons of ethanol per year which is about 25% of the present U.S. ethanol production. Thus, the required extension of the ethanol transportation fuel infrastructure is very modest. Moreover, with the substantial increase in E85 infrastructure as presently planned by the 2005 Energy Act, additional ethanol can be used as a substitute fuel in addition to its use as an on-demand octane boost agent.
An object of the present invention is to minimize the inconvenience and cost of using a separate tank for the on-demand octane boost agent. Another object is a fuel management system designed so as to reduce the additional cost of flexible fuel operation.